Recently, there has been an increasing tendency that hub unit bearings for wheels include a rotational speed detector having installed therein an encoder made up of a multipolar magnet and an active sensor employing a Hall element or MR element in association with spread of ABS (Anti-lock Brake System).
As seen in JP-A-2002-333033, for example, there is an increasing number of multipolar magnets incorporating encorders which has a construction in which an encoder is fabricated integrally into a seal of a bearing so as to be installed in a hub unit bearing as a seal with an encoder.
However, in the case of a hub unit bearing for a driven wheel, since a constant velocity joint for driving the wheel exits on a center side of a vehicle while lying adjacent to a hub unit bearing, a problem is caused that there is no space for installation of a sensor. There is a proposal to deal with this problem (for example, refer to Patent Document 1).
Patent Document 1 will be studied by the use of terms and reference numbers which are used in the document. In Patent Document 1, an encoder 29 is mounted on an outer circumference of a constant velocity joint 3, and a sensor 35 is mounted on a stationary member 1 so as to face the encoder 29, whereby a detecting portion is provided. This detecting portion is made to open to the inside of a vehicle body through a gap between a radially inner surface of the stationary member 1 and a radially outer surface of the constant velocity joint 3 and is regarded as a portion from which muddy water or the like tends to intrude into the inside of the vehicle body. Therefore, the gap is sealed on the inside of the vehicle body. Namely, a construction in which a sealing mechanism is provided on a center side of the vehicle body is adopted.
Patent Document 1: JP-A-2001-301590